Vehicles are typically equipped with an air conditioning system to provide cabin cooling and to dry air for dehumidifying functions. Air conditioning systems typically include a compressor driven by a vehicle's internal combustion engine. The compressor can be either engaged, fully or partially, or disengaged to the engine via an electronically controlled clutch.
During air conditioning system operation under certain operating conditions, the compressor cycles between an engaged and disengaged state. Cycling is typically controlled based on refrigerant pressure in the air conditioning system. When the engine and clutch are coupled, pressure decreases and significantly cooled cabin air is circulated through the vehicle. Such operation continues until pressure reaches a minimum value where the clutch is controlled to disengage the engine and compressor. If air circulation is continued, pressure increases until it reaches a maximum value. At this maximum value, the compressor is then re-engaged via the clutch and cycling repeats.
It is also known to disengage the engine and compressor during vehicle launch conditions, thereby allowing more engine output. In this way, degraded vehicle launch performance is avoided, even when air conditioning is operational. Vehicle launch is determined based on vehicle speed, throttle position, and various other factors.
The inventors herein have recognized disadvantages with the above approaches. First, driver comfort is degraded during clutch engagements during some driving conditions. In other words, during some driving conditions, clutch engagements are felt strongly by vehicle operators and comfort is therefore degraded.
Second, optimum fuel economy is not obtained since compressor cycling engagement is not coordinated to vehicle and engine operating conditions. In other words, during some conditions, extra fuel is added to the engine to provide air conditioning while maintaining engine output at a desired level. During other conditions, no extra fuel is needed to provide air conditioning.